1. Field of the Invention
The present invention generally relates to a curable inkjet ink composition for use in digital printing. More specifically, the present invention relates to a curable inkjet ink composition comprising a mono-functional monomer that can be directly printed onto a plastic substrate. The mono-functional monomer enables the ink composition to undergo continuous elongation during thermal processing of the plastic substrate. The present invention further includes methods of forming the curable inkjet ink composition, methods of using the curable inkjet composition, and articles formed using the curable inkjet composition.
2. Description of the Prior
Inkjet imaging techniques have become very popular in commercial and consumer applications. Inkjet printers typically operate by ejecting ink onto a receiving substrate in controlled patterns of closely spaced ink droplets. By selectively regulating the pattern of ink droplets, inkjet printers can produce a wide variety of printed features, including text, graphics, images, holograms, and the like.
Thermal inkjet printers and piezo inkjet printers are the two main types of inkjet systems in widespread use today. For both approaches, inks must meet stringent performance requirements in order for the inks to be appropriately jettable and for the resultant printed features to have the desired mechanical, chemical, visual, and durability characteristics.
Solvent-based and water-based jettable inks are well known. A typical water-based ink generally comprises water, a colorant, which may be a dye and/or a pigment, one or more co-solvents, and one or more additives that are included to enhance the performance of the ink. Representative examples of such additives include one or more colorants, slip modifiers, thixotropic agents, foaming agents, antifoaming agents, flow or other rheology control agents, waxes, oils, plasticizers, binders, antioxidants, fungicides, bactericides, organic and/or inorganic filler particles, leveling agents, opacifiers, antistatic agents, dispersants, and the like.
Solvent-based inks include relatively volatile, organic solvents. Such inks dry more rapidly than aqueous inks. However, such solvents may be toxic, flammable, or the like, requiring careful handling. In addition, the solvent-based inks also tend to be compatible with only a limited range of substrates.
In order to avoid using a conventional solvent, inks incorporating a polymerizable diluent have been developed. The diluent tends to function as a viscosity reducer, as a binder when cured, and optionally as a cross-linking agent. In the uncured state, the inks have a low viscosity and are readily jetted. However, the polymerizable diluents readily cross-link upon exposure to a suitable source of curing energy, for example ultraviolet light, electron beam energy, and/or the like, to form a cross-linked polymer network.
Inkjet inks are typically limited to digitally printing onto flat sheet constructions, such as papers, plastics, banner materials and the like. For plastic substrates or three-dimensional plastic constructions, screen printing was the preferred method since digital printing of inkjet inks onto plastic substrates produced images that cracked or could not elongate under thermal conditions. Therefore, there is a need to be able to digitally print directly onto plastic substrates using inkjet printing systems to form ink images capable of continual elongation during thermal processing.